The application of synthetic polymer chemistry to the field of sports equipment has revolutionized the performance of athletes in many sports. One sport in which this is particularly true is golf, especially as relates to advances in golf ball performance and ease of manufacture. For instance, the earliest golf balls consisted of a leather cover filled with wet feathers. These “feathery” golf balls were subsequently replaced with a single piece golf ball made from “gutta percha,” a naturally occurring rubber-like material. In the early 1900's, the wound rubber ball was introduced, consisting of a solid rubber core around which rubber thread was tightly wound with a gutta percha cover.
Subsequently, new cover materials were discovered and balata was used as the primary material for covers of golf balls until the 1960's when SURLYN®, an ionomeric resin made by E.I. DuPont de Nemours & Co. was introduced to the golf industry. SURLYN® costs less than balata and has a better cut resistance than balata. At the present time, SURLYN® is used as the primary source of cover stock for most two-piece and some three-piece golf balls. The problem with SURLYN®-covered golf balls, however, is that they lack the “click” and “feel” which golfers had become accustomed to with balata. “Click” is the sound made when the ball is hit by a golf club while “feel” is the overall sensation imparted to the golfer when the ball is hit. However, unlike SURLYN®-covered golf balls, polyurethane- or polyurea-covered golf balls can be made to have the “click” and “feel” of balata. Thus premium golf balls today typically exhibit polyurethane or polyurea covers, typically prepared by the reaction of a diisocyanate with a polyol (in the case of polyurethanes) or with a polyamine (in the case of a polyurea). Thermoplastic polyurethanes or polyureas may consist solely of this initial mixture or may be further combined with a chain extender to vary properties such as hardness of the thermoplastic. Thermoset polyurethanes or polyureas typically are formed by the reaction of a diisocyanate and a polyol or polyamine respectively, and an additional crosslinking agent to crosslink or cure the material to result in a thermoset.
In addition to golf ball materials, the construction of the golf ball has evolved over the years. Most modern golf balls can be classified as one-piece, two-piece, and three-piece. One-piece balls are molded from a homogeneous mass of material upon which is molded a dimple pattern. One-piece balls are inexpensive and very durable, but do not provide great distance because of relatively high spin and low velocity. Two-piece balls are made by molding a cover around a solid rubber core. These are the most popular types of balls in use today. In attempts to further modify the ball performance, especially in terms of the distance such balls travel, and the feel transmitted to the golfer through the club on striking the ball, the basic two piece ball construction has been further modified by the introduction of additional layers between the core and outer cover layer. If one additional layer is introduced between the core and outer cover layer, a so called “three-piece ball” results, and similarly, if two additional layers are introduced between the core and outer cover layer, a so called “four-piece ball” results, and so on.
In tandem with the development of golf ball materials and construction, the aerodynamic properties of golf balls have also been the subject of much development. The first golfers in the 1800's realized that gutta-percha golf balls with damaged or indented surfaces flew better than smooth new ones. Subsequently golf balls with brambles (bumps rather than dents), such as the Spalding Agrippa, or with grooves such as the Spalding Silvertown were popular from the late 1800's to 1908. In 1908, William Taylor, patented a golf ball with indentations (dimples) that flew better than golf balls with brambles or grooves. For the next 60 years most balls looked exactly the same having 336 dimples of the same size distributed in an octahedron or so-called Atti pattern over the surface. The ATTI pattern, named after its inventor Ralph Atti, was based on an octahedron, split into eight concentric straight line rows. The only other significant innovation related to the surface of a golf ball during this sixty year period came from Albert Penfold who invented a mesh-pattern golf ball for Dunlop. This pattern was invented in 1912 and was accepted until the 1930's.
In the 1970's, additional dimple patterns were introduced which attempted to maximize the surface coverage of dimples on the ball. For example U.S. Pat. No. 4,949,976 to William Gobush discloses a golf ball with 78% dimple coverage with up to 422 dimples. The 1990's have also seen the dimple surface area coverages increase to up to 80%.
In addition to maximizing surface coverage, recent innovations in dimple pattern design have seen the number of different dimples on a golf ball surface increase both in the variety of their diameters and/or depths. These have included dimple patterns with four or five to as many as eleven different dimple sizes. Additionally, dimple patterns have been based on other sectional shapes, such as pentagonal, as in U.S. Pat. No. 5,201,522, octahedral, dodecahedral and icosahedral patterns or modified versions of these such as in U.S. Pat. No. 4,880,241 which disclose a golf ball dimple pattern having a modified icosahedron pattern.
More recently there have been a number of patents which have attempted to not only maximize surface coverage but also impart selected lift and drag properties for the golf ball. For instance, a drag penalty is often incurred when a single row of deep dimples are placed adjacent to the seam and U.S. Pat. No. 6,066,055 describes how arranging dimple volume differently in (latitudinal) regions is beneficial in producing better ball symmetry, or anisotropy, in flight as compared to a single row of deep dimples near the seam.
Of course the aerodynamic properties imparted by a selected dimple pattern may result in one trajectory for a professional golfer, who would typically have a much higher swing speed than a less accomplished amateur golfer with a slower swing speed. In addition, professional golfers with higher swing speeds also typically impart higher spin on the ball. However to date there is little information on how a given dimple arrangement may be tailored to produce a desired trajectory and which also takes into account the different spin rates imparted to the ball as a result of the golfers swing profile.
This invention offers a dimple design with superior performance in carry distance for golfers whose swing profile generates moderate to low ball spin rates defined here to be from about 1500 rpm to 2600 rpm. This has been achieved by both reducing drag on the overall ball, while increasing lift judiciously. Three separate design features are employed in combination to achieve these results. The first is a method of arranging dimple volume that compensates for seam effects on the ball, the second is reducing total dimple volume (TDV) to the appropriate limit, and the third is selecting a specific dimple volume ratio (VR) with low drag characteristics.